<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<div id="app">
   <button @click="sub">-
   </button>
    <span v-text="num"></span>
    <button @click="add">+
    </button>
</div>
<!-- 开发环境版本，包含了有帮助的命令行警告 -->
<script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
<script>
    var app=new Vue({
        el:"#app",
        data:{
          num:1
        },
        methods:{
            add:function () {
                if (this.num<10) {
                this.num++;
                    }else {
                    alert("不要点了，已经到最大值了");
                }
            },
            sub:function () {
                if (this.num>1) {
                    this.num--;
                }else {
                    alert("已经到最小值了");
                }
            }
        }
    })
</script>
</body>
</html>